1. Field of the Invention
The present invention relates to a stepper mechanism for transporting a substrate along a linear transport path, comprising a stationary member and first and second transport members extending widthwise across the transport path, said stationary member and transport members each being adapted to alternatingly grip and release the substrate, and independent drive units arranged on either side of the transport path for moving the respective ends of the transport members in a transport direction.
2. Description of Background Art
A stepper mechanism of this kind may be used, for example, for transporting print substrates in the form of separate sheets or endless webs through a printer, e.g. over a print surface of an ink jet printer.
In comparison with roller-type transport mechanisms for print substrates, wherein the substrate is passed through a nip between two rollers, a stepper mechanism has the advantage that it is intrinsically less prone to micro-slip and is not affected by inaccuracies resulting from the geometry and/or eccentricity of a transport roller, and the like, so that a very high step accuracy can be achieved. Moreover, since the stepper mechanism may be arranged to engage the substrate only from one side, preferably the side opposite to the side on which an image is printed, it is capable of handling a large variety of different types of substrates having different thickness and being made of different materials including both flexible and rigid materials, without affecting the image that is being printed or has just been printed on the substrate.
Since the drive systems arranged on opposite sides of the transport path are independent from one another, a possible misalignment of the substrate may be corrected by providing different step widths for the left and right sides of the substrate.
A known stepper mechanism of the type described above has been disclosed in Research Disclosure 36449, published in August 1994. In this mechanism, the two transport members are rigidly connected to one another, so that they form a rectangular frame which encloses the stationary member with sufficient space available in the transport direction, so that the frame may be moved relative to the stationary member.